A sacral Tarlov cyst is a fluid-filled sac that forms on the nerve roots at the base of your spine, in the bone called the sacrum. These cysts sit within the nerve root sheath and contain cerebrospinal fluid, the same liquid that surrounds your brain and spinal cord. About 4% of the population has one, and the vast majority never know it. Most Tarlov cysts are discovered by accident on an MRI ordered for something else entirely.
How Tarlov Cysts Form
Your spinal cord sends out nerve roots that branch into the rest of your body, and each root is wrapped in layers of protective tissue. A Tarlov cyst develops when cerebrospinal fluid collects between these tissue layers, creating a pocket that slowly expands. What makes these cysts distinct from other spinal cysts is that nerve root fibers are embedded in the cyst wall or float inside the cyst cavity. This is what separates them from simpler fluid collections that don’t involve nerve tissue.
The leading theory for why they grow involves a one-way valve effect. Cerebrospinal fluid flows into the cyst during normal pressure changes (like coughing, straining, or standing up), but has difficulty draining back out. Imaging studies confirm this: contrast dye injected into the spinal fluid shows delayed flow into the cyst and delayed flow out. Over time, this trapping mechanism allows the cyst to gradually enlarge, sometimes eroding into the surrounding bone.
Who Gets Them and How Common They Are
A large meta-analysis covering over 13,000 subjects found a global prevalence of about 4.18%. Of those cysts, only about 15.6% correspond with symptoms, which means the overwhelming majority are silent. Other estimates put the symptomatic rate even lower, at 5% to 8% of diagnosed cases. Women are diagnosed more often than men, though it’s not entirely clear whether women develop them more frequently or simply undergo more pelvic and spinal imaging.
Symptoms of a Symptomatic Cyst
When a Tarlov cyst does cause problems, the symptoms reflect its location on sacral nerve roots. These nerves control sensation and function in your lower back, legs, pelvis, bladder, and bowels. The most common complaint is radicular pain: a burning, shocking, or shooting sensation that travels from the lower back down through the legs. Nearly all symptomatic patients experience this type of pain.
Beyond pain, symptoms can include:
- Numbness or weakness in the legs or feet
- Bladder and bowel changes such as difficulty urinating, increased frequency, or constipation (reported in about 50% of symptomatic cases)
- Perineal pain, felt in the area between the genitals and the anus (about 10% of symptomatic cases)
- Sexual dysfunction
- Headaches, particularly when the cyst is large enough to affect cerebrospinal fluid dynamics
Symptoms often worsen with activities that increase spinal fluid pressure: prolonged sitting, standing, coughing, sneezing, or lifting. Larger cysts are generally more likely to cause symptoms, partly because they compress more nerve tissue and partly because they can erode into the sacral bone itself, a finding called bony scalloping that shows up clearly on imaging.
How Tarlov Cysts Are Diagnosed
MRI is the primary tool. On an MRI, a Tarlov cyst appears as a well-defined, thin-walled sac filled with fluid that matches the brightness of cerebrospinal fluid. Radiologists look for several features: the size of the cyst in multiple dimensions, whether it’s eroding into bone, whether it’s narrowing the openings where nerves exit the spine, and whether it’s compressing nerve roots.
Under the Nabors classification system for spinal cysts, Tarlov cysts fall into the Type II category, meaning they are extradural (outside the main spinal fluid sac) and contain nerve root fibers. This classification matters because other sacral cysts exist that look similar on MRI but don’t contain nerve tissue. These non-Tarlov cysts tend to appear as single, larger masses and are more likely to cause neurological deficits like leg weakness, while Tarlov cysts more often appear as multiple smaller cysts and present primarily with pain. Definitively confirming nerve fibers within the cyst wall sometimes requires surgical visualization under a microscope.
Conservative Treatment Options
Because most Tarlov cysts don’t cause symptoms, the first approach for many people is simply monitoring. If your cyst was found incidentally and you have no pain or functional problems, treatment is rarely needed.
For symptomatic cysts, initial management typically involves a combination of pain-relieving and nerve-calming medications, anti-inflammatory drugs, and physical therapy. The goal is to manage nerve-related pain and maintain function. Physical therapy focuses on core stability and movement strategies that reduce pressure on the sacral area. Many people find adequate relief through these measures and never require a procedure.
Minimally Invasive Procedures
When conservative treatment isn’t enough, one option is CT-guided percutaneous aspiration with fibrin sealant injection. In this procedure, a needle is guided into the cyst under CT imaging, the fluid is drained, and a biological glue is injected to seal the cyst and prevent refilling.
A study of 213 patients who underwent this procedure found that 81.8% were satisfied with the outcome at one year, with 54.2% reporting excellent results. At three to six years of follow-up, satisfaction dropped somewhat to 74%, though the percentage reporting excellent results actually increased slightly to about 60%. The main limitation is recurrence. About 10.8% of patients needed a repeat procedure within the first six months because their cysts refilled, and another 6.1% needed re-aspiration later. Repeat MRI in those cases confirmed the fluid had reaccumulated.
Surgical Treatment
Surgery is reserved for cases where symptoms are significant and less invasive options have failed. The procedure involves a partial sacral laminectomy, where a portion of bone is removed to expose the cyst. From there, surgeons use one of two main techniques: wrapping the cyst with a dural substitute material to contain it, or resecting (removing) the cyst and closing the opening.
A study of 97 consecutive surgical patients found that 76% experienced meaningful improvement. The wrapping technique and the resection technique produced similar rates of symptom relief (about 79% versus 63%, though this difference wasn’t statistically significant). However, cyst recurrence was significantly more common after resection: 29.4% compared to 8.8% with wrapping.
Surgery carries real risks. The overall complication rate in that study was 17.5%. The most common complication was cerebrospinal fluid leaking from the surgical site, affecting about 10% of patients. More serious but rare complications included cauda equina syndrome (a condition involving loss of nerve function in the lower body), wound infection, meningitis, persistent headaches, and genital numbness. These risks are part of why surgery is typically a last resort, and why finding a surgeon experienced specifically with Tarlov cysts matters.
Living With an Asymptomatic Cyst
If you’ve been told you have a Tarlov cyst after a routine MRI, the odds are strongly in your favor that it will never cause problems. The critical question is whether your current symptoms, if you have any, actually match what a sacral nerve root cyst would produce. Lower back pain is extremely common and has dozens of causes, so a Tarlov cyst found on imaging isn’t automatically the explanation. The cyst’s size, its relationship to nearby nerve roots, and whether there’s bony erosion all factor into whether it’s likely the source of your symptoms or simply a bystander.